Ecdysone Synthesis Research Articles

YTHDF3 Is Involved in the Diapause Process of Bivoltine Bombyx mori Strains by Regulating the Expression of Cyp307a1 and Cyp18a1 Genes in the Ecdysone Synthesis Pathway.

The variable diapause features of bivoltine silkworm (Bombyx mori) strains regulated by environmental signals in the embryonic stage are closely related to epigenetics. Previously, we showed that the expression of YTHDF3 is significantly different in the pupae of the bivoltine silkworm Qiufeng developed from eggs incubated at a normal temperature (QFHT, diapause egg producer) compared to those from eggs incubated at a low temperature (QFLT, nondiapause egg producer), indicating that the expression of diapause-associated genes is regulated by the m6A modification level. However, how YTHDF3 regulates the expression of diapause-related genes remains unclear. In this study, we observed that the knockdown of B. mori YTHDF3 resulted in delayed embryo development, while the overexpression of YTHDF3 resulted in the transformation of nondiapause-destined eggs into a mixture of diapause and nondiapause eggs. Further studies showed that YTHDF3, as a reading protein, can recognize the m6A site of Cyp307a1 and Cyp18a1 genes in the ecdysone synthesis pathway (ESP), and the overexpression of YTHDF3 affects the diapause traits of the silkworm by decreasing the stabilities of mRNAs of Cyp307a1 and Cyp18a1 and inhibiting their translation. The above results demonstrate that m6A modification mediates YTHDF3 to affect the expression levels of its target genes, Cyp307a1 and Cyp18a1, in the ESP to regulate diapause in bivoltine B. mori. This is the first report of the m6A methylation regulation mechanism in diapause in B. mori and provides new experimental data for clarifying the diapause regulation network.

Early-Stage Defense Mechanism of the Cotton Aphid Aphis gossypii Against Infection With the Insect-Killing Fungus Beauveria bassiana JEF-544.

Aphis gossypii, commonly known as the cotton aphid, is a widely distributed pest of agricultural crops and acts as a vector for many serious plant viruses. Cotton aphid shows high resistance to chemical insecticides due to rapid rates of genetic diversity as a result of its short life cycle, seasonal migration, and host alteration. As an alternative, entomopathogenic fungi can be used to control cotton aphids in an environmentally sound manner. However, little is known about how cotton aphids respond to fungal infection. In this work, a new Beauveria bassiana strain JEF-544 (Bb JEF-544) was selected and isolated through bioassays with high virulence against cotton aphid. Early response of cotton aphid to Bb JEF-544 infection was analyzed at the transcriptome level. Infected aphids were collected two days after treatment at 25% lethal time (LT25), and total RNA of non-infected and Bb JEF-544-infected aphids was independently subjected to sequencing. Infected aphids showed significant up-regulation of the insect hormone biosynthesis pathway. Bursicon (Burs) and crustacean cardioactive peptide (CCAP) receptors involved in molting along with ecdysone synthesis were also strongly up-regulated in the aphid response to the fungal infection. In the immune response, melanization in the hemocoel was significantly up-regulated, while phagocytosis was less actively transcribed. In conclusion, cotton aphids protect themselves from Bb JEF-544 infection by activating the immune response including melanization and insect molting hormones to shed infected cuticles. In addition to describing the initial stages of Bb JEF-544 infection at the transcriptome level, this work provides potential treatment targets and insight into how fungal isolates can effectively be used to control this serious aphid species.

Functional characterization of a low-density lipoprotein receptor in the lepidopteran model, Bombyx mori.

The growth and development of metabolous insects are mainly regulated by ecdysone and juvenile hormone. As a member of the low-density lipoprotein receptor (LDLR) family, megalin (mgl) is involved in the lipoprotein transport of cholesterol which is an essential precursor for the synthesis of ecdysone. Despite extensive studies in mammals, the function of mgl is still largely unknown in insects. In this study, we characterize the function of mgl in the silkworm Bombyx mori, the model species of Lepidoptera. We find that mgl is broadly present in the genomes of lepidopteran species and evolved with divergence between lepidopterans and Drosophila. The expression pattern suggests a ubiquitous role of mgl in the growth and development in the silkworm. We further perform clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9-based mutagenesis of Bmmgl and find that both the development and the silk production of the silkworm are seriously affected by the disruption of Bmmgl. Our results not only explore the function of mgl in Lepidoptera but also add to our understanding of how cholesterol metabolism is involved in the development of insects.

Maf regulates the overexpression of CYP307A1, which is involved in the fitness advantage of bistrifluron-resistant Spodoptera litura (Fab.) (Noctuidae: Lepidoptera)

Spodoptera litura is a widely distributed multifeeding pest, that has developed high resistance to many chemical insecticides. In the present study, a bistrifluron-resistant (Bis-SEL) strain showing 113.8-fold resistance ratio relative to a bistrifluron-susceptible (Bis-UNSEL) strain was obtained and showed a fitness advantage (resurgence). First, we found that the observed resurgence might have resulted from Maf transcription factor overexpression in the Bis-SEL strain, which would influence the synthesis of ecdysone and chitin. Additionally, a co-expression relationship between Maf and CYP307A1 was verified by weighted correlation network analysis (WGCNA) and qRT–PCR, and the expression of CYP307A1, a key gene in ecdysone synthesis, was significantly downregulated by Maf interference. The assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) and a yeast one-hybrid showed that Maf could bind to the cncc:maf-s element in the CYP307A1 promoter region. The synthesis of ecdysone, which stimulated chitin synthesis, was also decreased significantly following Maf and CYP307A1 interference. Therefore, the upregulation of Maf expression leaded to the upregulation CYP307A1 expression, which led to an increase in the synthesis of ecdysone, resulting in resurgence accompanied by resistance to bistrifluron.

The steroid hormone ecdysone regulates growth rate in response to oxygen availability

In almost all animals, physiologically low oxygen (hypoxia) during development slows growth and reduces adult body size. The developmental mechanisms that determine growth under hypoxic conditions are, however, poorly understood. Here we show that the growth and body size response to moderate hypoxia (10% O2) in Drosophila melanogaster is systemically regulated via the steroid hormone ecdysone. Hypoxia increases level of circulating ecdysone and inhibition of ecdysone synthesis ameliorates the negative effect of low oxygen on growth. We also show that the effect of ecdysone on growth under hypoxia is through suppression of the insulin/IGF-signaling pathway, via increased expression of the insulin-binding protein Imp-L2. These data indicate that growth suppression in hypoxic Drosophila larvae is accomplished by a systemic endocrine mechanism that overlaps with the mechanism that slows growth at low nutrition. This suggests the existence of growth-regulatory mechanisms that respond to general environmental perturbation rather than individual environmental factors.

Ecdysone exerts biphasic control of regenerative signaling, coordinating the completion of regeneration with developmental progression

In Drosophila melanogaster, loss of regenerative capacity in wing imaginal discs coincides with an increase in systemic levels of the steroid hormone ecdysone, a key coordinator of their developmental progression. Regenerating discs release the relaxin hormone Dilp8 (Drosophila insulin-like peptide 8) to limit ecdysone synthesis and extend the regenerative period. Here, we describe how regenerating tissues produce a biphasic response to ecdysone levels: lower concentrations of ecdysone promote local and systemic regenerative signaling, whereas higher concentrations suppress regeneration through the expression of broad splice isoforms. Ecdysone also promotes the expression of wingless during both regeneration and normal development through a distinct regulatory pathway. This dual role for ecdysone explains how regeneration can still be completed successfully in dilp8- mutant larvae: higher ecdysone levels increase the regenerative activity of tissues, allowing regeneration to reach completion in a shorter time. From these observations, we propose that ecdysone hormone signaling functions to coordinate regeneration with developmental progression.

Growth Regulating Effects of Natural Pesticide, Azadirachtin from Neem Tree (Azadirachta indica A. Juss) on Insects: A Review

Azadirachtin is a tetranortriterpenoid derived from the neem tree Azadirachta indica A. juss. Azadirachtin has attracted worldwide attention as promising feeding deterrent, insect growth disruptor and sterilent. Azadirachtin based pesticides become very much popular because of its biodegradability and least toxicity to non- target organisms. It has now been promoted as an alternative insecticide in integrated pest management programmes. Azadirachtin has an ability to modify or suppress haemolymph ecdysteroid and juvenile hormone titres through inhibition of the secretion of brain peptides prothoracicotropic hormone and allatotropic hormone, which are responsible for inducing the synthesis and release of ecdysone from the prothoracic gland and juvenile hormone from corpora allata, respectively. Blocking the synthesis and release of ecdysone and juvenile hormone leading to disruption of coordination of moulting process. Furthermore, this compound is known to cause degenerative changes in the cells of insect endocrine glands. This review focuses on growth regulating effects of natural pesticide, azadirachtin from neem tree (Azadirachta indica A. Juss) on insects.

Transcription factors CncC and Maf connect the molecular network between pesticide resistance and resurgence of pest mites.

Pesticide resistance and resurgence are serious problems often occurring simultaneously in the field. In our long-term study of a fenpropathrin-resistant strain of Tetranychus cinnabaribus, enhancement of detoxification and modified fecundity mechanisms were both observed. Here we investigate the network across these two mechanisms and find a key node between resistance and resurgence. We show that the ecdysone pathway is involved in regulating the fecundity of T. cinnabaribus. The concentration change of ecdysone is consistent with the fecundity curve; the concentration of ecdysone is higher in the fenpropathrin-resistant strain which has stronger fecundity. The enhancement of ecdysone is due to overexpression of two P450 genes (CYP314A1 and CYP315A1) in the ecdysone synthesis pathway. Silencing expression of these CYP genes resulted in lower concentration of ecdysone, reduced expression of vitellogenin, and reduced fecundity of T. cinnabaribus. The expression of CYP315A1 is regulated by transcription factors Cap-n-collar isoform C (CncC) and Musculoaponeurotic fibrosarcoma protein (Maf), which are involved in regulating other P450 genes functioning in detoxification of fenpropathrin in T. cinnabaribus. A similar regulation is established in citrus pest mite Panonychus citri showing that the CncC pathway regulates expression of PcCYP315A1, which affects mite fecundity. Transcription factors are activated to upregulate detoxification genes facilitating pesticide resistance, while the "one to multiple" regulation mode of transcription factors simultaneously increases expression of metabolic enzyme genes in hormone pathways and alters the physiology of pests. This is an important response of arthropods to pesticides which leads to resistance and population resurgence.

Ecdysone regulates Drosophila wing disc size via a TORC1 dependent mechanism

Most cells in a developing organ stop proliferating when the organ reaches a correct, final size. The underlying molecular mechanisms are not understood. We find that in Drosophila the hormone ecdysone controls wing disc size. To study how ecdysone affects wing size, we inhibit endogenous ecdysone synthesis and feed larvae exogenous ecdysone in a dose-controlled manner. For any given ecdysone dose, discs stop proliferating at a particular size, with higher doses enabling discs to reach larger sizes. Termination of proliferation coincides with a drop in TORC1, but not Dpp or Yki signaling. Reactivating TORC1 bypasses the termination of proliferation, indicating that TORC1 is a main downstream effector causing proliferation termination at the maximal ecdysone-dependent size. Experimental manipulation of Dpp or Yki signaling can bypass proliferation termination in hinge and notum regions, but not the pouch, suggesting that the mechanisms regulating proliferation termination may be distinct in different disc regions.

Influence of an elevated CO2level on life history parameters and hormone pathway or vitellogenin metabolism of the brown planthopper

AbstractThe growth, development and reproduction of herbivorous insects could be altered due to changes in quality and quantity of their host plants under elevated CO2. The brown planthopper,Nilaparvata lugens, is one of the most serious and destructive economic pests in rice growing areas in Asia. In this study, we investigated the effect of elevated CO2on the growth, development and reproduction ofN. lugensand, in particular, on the hormonal regulation of the transcription factors inN. lugens. The results indicated that compared with ambient CO2, elevated CO2significantly shortened the duration of egg and nymph, longevity of female adults and total adults, and significantly decreased the weight of adults; besides, elevated CO2significantly improved the fecundity of female adults, egg hatching rata and the transcription levels ofVg. The relative expression levels ofJHMAT‐andFAMeT‐regulated synthesis of JH were first down‐regulated and then up‐regulated with the development of the 5th instar nymph ofN. lugensunder elevated CO2. In addition, the relative expression level ofcyp314a1played an important role in synthesis of ecdysone was up‐regulated in the 5th instar nymph ofN. lugensunder elevated CO2. We have demonstrated that elevated CO2could accelerate the development and improve the reproduction ofN. lugens, which is related to the transcription levels of JH, MH and Vg.

IP3-mediated Ca2+ signals regulate larval to pupal transition under nutrient stress through the H3K36 methyltransferase Set2.

Persistent loss of dietary protein usually signals a shutdown of key metabolic pathways. In Drosophila larvae that have reached a 'critical weight' and can pupariate to form viable adults, such a metabolic shutdown would needlessly lead to death. Inositol 1,4,5-trisphosphate-mediated calcium (IP3/Ca2+) release in some interneurons (vGlutVGN6341) allows Drosophila larvae to pupariate on a protein-deficient diet by partially circumventing this shutdown through upregulation of neuropeptide signaling and the expression of ecdysone synthesis genes. Here, we show that IP3/Ca2+ signals in vGlutVGN6341 neurons drive expression of Set2, a gene encoding Drosophila Histone 3 Lysine 36 methyltransferase. Furthermore, Set2 expression is required for larvae to pupariate in the absence of dietary protein. IP3/Ca2+ signal-driven Set2 expression upregulates key Ca2+-signaling genes through a novel positive-feedback loop. Transcriptomic studies, coupled with analysis of existing ChIP-seq datasets, identified genes from larval and pupal stages that normally exhibit robust H3K36 trimethyl marks on their gene bodies and concomitantly undergo stronger downregulation by knockdown of either the intracellular Ca2+ release channel IP3R or Set2. IP3/Ca2+ signals thus regulate gene expression through Set2-mediated H3K36 marks on select neuronal genes for the larval to pupal transition.

Olfactory perception of herbicide butachlor by GOBP2 elicits ecdysone biosynthesis and detoxification enzyme responsible for chlorpyrifos tolerance in Spodoptera litura

Insecticide resistance is one of the major obstacles for controlling agricultural pests. There have been a lot of studies on insecticides stimulating the development of insect resistance. Herbicides account for the largest sector in the agrochemical market and are often co-applied with insecticides to control insect pests and weeds in the same cropland ecosystem. However, whether and how herbicides exposure will affect insecticide resistance in insect pests is largely unexplored. Here we reported that after exposure to herbicide butachlor, the lepidopteran Spodoptera litura larvae reduced susceptibility to the insecticide chlorpyrifos. Docking simulation studies suggested that general odorant-binding protein 2 (GOBP2) could bind to butachlor with high binding affinity, and silencing SlGOBP2 by RNA interference (RNAi) decreased larval tolerance to chlorpyrifos. Butachlor exposure induced ecdysone biosynthesis, whose function on increasing chlorpyrifos tolerance was supported in synergism experiments and confirmed by silencing the key gene (SlCYP307A1) for ecdysone synthesis. Butachlor exposure also activated the expression of detoxification enzyme genes. Silencing the genes with the highest herbicide-induced expression among the three detoxification enzyme genes led to increased larval susceptibility to chlorpyrifos. Collectively, we proposed a new mechanism that olfactory recognition of herbicides by GOBP2 triggers insect hormone biosynthesis and leads to high metabolic tolerance against insecticides. These findings provide valuable information for the dissection of mechanisms of herbicide-induced resistance to insecticides and also supplements the development of reduced-risk strategies for pest control.

Azadirachtin interferes with basal immunity and microbial homeostasis in the Rhodnius prolixus midgut

Rhodnius prolixus is an insect vector of two flagellate parasites, Trypanosoma rangeli and Trypanosoma cruzi, the latter being the causative agent of Chagas disease in Latin America. The R. prolixus neuroendocrine system regulates the synthesis of the steroid hormone ecdysone, which is essential for not only development and molting but also insect immunity. Knowledge for how this modulates R. prolixus midgut immune responses is essential for understanding interactions between the vector, its parasites and symbiotic microbes. In the present work, we evaluated the effects of ecdysone inhibition on R. prolixus humoral immunity and homeostasis with its microbiota, using the triterpenoid natural product, azadirachtin. Our results demonstrated that azadirachtin promoted a fast and lasting inhibitory effect on expression of both RpRelish, a nuclear factor kappa B transcription factor (NF-kB) component of the IMD pathway, and several antimicrobial peptide (AMP) genes. On the other hand, RpDorsal, encoding the equivalent NF-kB transcription factor in the Toll pathway, and the defC AMP gene were upregulated later in azadirachtin treated insects. The treatment also impacted on proliferation of Serratia marcescens, an abundant commensal bacterium. The simultaneous administration of ecdysone and azadirachtin in R. prolixus blood meals counteracted the azadirachtin effects on insect molting and also on expression of RpRelish and AMPs genes. These results support the direct involvement of ecdysone in regulation of the IMD pathway in the Rhodnius prolixus gut.

Larval feeding status regulates the transcript levels of genes encoding PTTH and allatoregulatory peptides in silkworm Bombyx mori.

In Bombyx mori, two dorsolateral neurosecretory cells (NSCs) in each of the two brain lobes have been identified as prothoracicotropic hormone (PTTH) producing cells. This neuropeptide in insects stimulates the prothoracic gland for the synthesis and release of ecdysone, responsible for the molting events. Allatotropin (AT) and allatostatin (AST) are allatoregulatory neuropeptides that regulate juvenile hormone biosynthesis. Here, by using RT-qPCR, we showed that in B. mori, nutritional stress modulates the mRNA expression of AT and AST-C (allatostain type C) in the central nervous system consisting of the brain lobes and all the associated ganglia. Using whole-mount in situ hybridization, we showed that the feeding status of Bombyx larvae also influences the expression of PTTH in the NSCs of the brain. Food deprivation significantly decreased the mRNA expression levels of PTTH in larvae at active or terminal growth period. Further, we showed that insulin modulates the expression level of PTTH. However, its action was dependent on the feeding status of the larvae. At feeding, the insulin decreased the PTTH expression level, while at food deprivation, the insulin increased the PTTH expression level. The data thus indicates that larval feeding status plays an important role in altering the mRNA expression levels of allatoregulatory peptide genes and PTTH.

Detection of 7-Dehydrocholesterol and Vitamin D3 Derivatives in Honey.

20(S)-Hydroxyvitamin D3 (20(OH)D3) is an endogenous metabolite produced by the action of CYP11A1 on the side chain of vitamin D3 (D3). 20(OH)D3 can be further hydroxylated by CYP11A1, CYP27A1, CYP24A1 and/or CYP27B1 to several hydroxyderivatives. CYP11A1 also hydroxylates D3 to 22-monohydroxyvitamin D3 (22(OH)D3), which is detectable in the epidermis. 20-Hydroxy-7-dehydrocholesterol (20(OH)-7DHC) has been detected in the human epidermis and can be phototransformed into 20(OH)D3 following the absorption of ultraviolet B (UVB) energy by the B-ring. 20(OH)D3 and its hydroxyderivatives have anti-inflammatory, pro-differentiation and anti-proliferative effects, comparable to 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Since cytochromes P450 with 20- or 25-hydroxylase activity are found in insects participating in ecdysone synthesis from 7-dehydrocholesterol (7DHC), we tested whether D3-hydroxyderivatives are present in honey, implying their production in bees. Honey was collected during summer in the Birmingham area of Alabama or purchased commercially and extracted and analyzed using LC-MS. We detected a clear peak of m/z = 423.324 [M + Na]+ for 20(OH)D3 corresponding to a concentration in honey of 256 ng/g. We also detected peaks of m/z = 383.331 [M + H − H2O]+ for 20(OH)-7DHC and 25(OH)D3 with retention times corresponding to the standards. We further detected species with m/z = 407.329 [M + Na]+ corresponding to the RT of 7DHC, D3 and lumisterol3 (L3). Similarly, peaks with m/z = 399.326 [M + H − H2O]+ were detected at the RT of 1,25(OH)2D3 and 1,20-dihydroxyvitamin D3 (1,20(OH)2D3). Species corresponding to 20-monohydroxylumisterol3 (20(OH)L3), 22-monohydroxyvitamin D3 (22(OH)D3), 20,23-dihydroxyvitamin D3 (20,23(OH)2D3), 20,24/25/26-dihydroxyvitamin D3 (20,24/25/26(OH)2D3) and 1,20,23/24/25/26-trihydroxyvitamin D3 (1,20,23/24/25/26(OH)3D3) were not detectable above the background. In conclusion, the presence of 7DHC and D3 and of species corresponding to 20(OH)-7DHC, 20(OH)D3, 1,20(OH)2D3, 25(OH)D3 and 1,25(OH)2D3 in honey implies their production in bees, although the precise biochemistry and photochemistry of these processes remain to be defined.

BPA and its analogues (BPS and BPF) modify the expression of genes involved in the endocrine pathway and apoptosis and a multi drug resistance gene of the aquatic midge Chironomus riparius (Diptera)

Many countries are limiting the use of bisphenol A (BPA) because evidence shows it is dangerous to human health and wildlife. For the manufacturing of polycarbonate plastics, bisphenol S (BPS) and bisphenol F (BPF) are proposed as safer alternatives. They have already been released into the aquatic environment without previously available information about their potential adverse effects. In this study, we compared the effects of BPA, BPS and BPF exposure to the expression profile of genes involved in the endocrine pathway (EcR and E74), ecdysone metabolism (Cyp18a1 and Shadow), apoptosis (DRONC) and the multidrug resistance-associated protein 1 gene (MRP1) in the midge, Chironomus riparius (Diptera). The three toxicants increased Shadow expression, which is involved in ecdysone synthesis, but only BPF significantly altered Cyp18a1, which is implicated in ecdysone degradation. BPS and BPF modified EcR and E74 expression; BPF upregulated the effector caspase DRONC. Furthermore, BPA significantly increased MRP1 expression. This study provides insights into the action of bisphenols at the molecular level and highlights the potential risks of BPS and BPF as BPA alternatives.

Comparative analysis of the ecological fitness and transcriptome between two genotypes of the brown planthopper Nilaparvata lugens

Insect quantity is an important index for determining the degree of damage to plants. The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most important rice pests in Asia. Here, we used two genotypes of BPH, a high-fecundity genotype (HFG) and a low-fecundity genotype (LFG), to measure their ecological fitness and to explore possible causes for genotype differentiation by transcriptome sequencing. Our results showed that there were significant differences in body weight, egg hatching rate and honeydew secretion between the HFG and LFG, particularly, the number of eggs laid per female was more significant. Transcriptional analysis showed that a total of 1966 differentially expressed genes (DEGs) were mainly involved in energy metabolism, carbohydrate and lipid synthesis, insect hormone synthesis and fecundity-related pathways. Moreover, we found that the phosphorylation levels of AMPK, AKT and FoxO and the synthesis of ecdysone were different between the two genotypes of BPH. These findings may partially explain the difference in the ecological fitness between HFG and LFG. This study is the first to compare the differences between two genotypes of BPH and to provide transcriptomic evidence to further understand the fecundity of BPH.

Activated Ras/JNK driven Dilp8 in imaginal discs adversely affects organismal homeostasis during early pupal stage in Drosophila, a new checkpoint for development.

Dilp8-mediated inhibition of ecdysone synthesis and pupation in holometabolous insects maintains developmental homeostasis through stringent control of timing and strength of molting signals. We examined reasons for normal pupation but early pupal death observed in certain cases. Overexpression of activated Ras in developing eye/wing discs inhibited Ptth expression in brain via upregulated JNK signaling mediated Dilp8 secretion from imaginal discs, which inhibited ecdysone synthesis in prothoracic gland after pupariation, leading to death of ~25- to 30-hour-old pupae. Inhibition of elevated Ras signaling completely rescued early pupal death while post-pupation administration of ecdysone to organisms with elevated Ras signaling in eye discs partially rescued their early pupal death. Unlike the earlier known Dilp8 action in delaying pupation, hyperactivated Ras mediated elevation of pJNK signaling in imaginal discs caused Dilp8 secretion after pupariation. Ectopic expression of certain other transgene causing pupal lethality similarly enhanced pJNK and early pupal Dilp8 levels. Suboptimal ecdysone levels after 8 hours of pupation prevented the early pupal metamorphic changes and caused organismal death. Our results reveal early pupal stage as a novel Dilp8 mediated post-pupariation checkpoint and provide further evidence for interorgan signaling during development, wherein a peripheral tissue influences the CNS driven endocrine function.

Gene expression profiling of ovary identified eggshell proteins regulated by 20-hydroxyecdysone in Bactrocera dorsalis

The oriental fruit fly, Bactrocera dorsalis, is one of the most destructive pests worldwide. The frequent use of chemical insecticides has led B. dorsalis to develop resistance to many insecticides in recent decades. New high-throughput-sequenced transcriptomes, as well as genomes, have revealed a large number of reference genes for functional target identification. Here, we performed digital gene expression profiling of ovary and testis of B. dorsalis adults. Various genes were identified to be highly expressed in B. dorsalis ovary. The genes encoding components of eggshell, vitelline membrane proteins (Vmps) and chorion-related proteins, were identified to be tissue-specifically expressed in ovary. Five cytochrome P450 genes were also identified to be highly expressed in ovary. Three of them were ecdysone synthesis pathway genes indicating the ovary as a potential synthesis site of female. The up-regulated expression of Vmps by exogenous 20-hydroxyecdysone implied the hormonal regulation of eggshell formation during ovarian development. Many other genes with potential functions in ovarian development were also identified, including vitellogenin receptor, insulin receptor, NASP protein, and odorant binding protein. These findings should promote our understanding of the regulation of vitellogenesis and eggshell formation and enable exploration of potentially novel pest control targets.

Relative expression of three key genes involved in the hormonal cycle of the freshwater amphipod, Gammarus pulex.

Ecdysteroids and sesquiterpenoids are the two groups of hormones controlling molt and growth processes in amphipods, and are mostly represented by ecdysone (i.e., 20-hydroxyecdysone) and methyl farnesoate (MF), respectively. The endocrine system responsible for their syntheses is located in the cephalothorax and is composed of three main organs: the X-organ/sinus gland complex (XO), the Y-organ (YO) and the mandibular organ. Ecdysone synthesis is negatively controlled by the molt-inhibiting hormone (MIH) produced by XO, and its signal is mediated through the ecdysteroid receptor (EcR); whereas the MF production is limited by the farnesoic acid O-methyltransferase enzyme (FAMeT). As little is known on MIH, EcR, and FAMeT in amphipods, this study focused on the evaluation of the expression variations of the gene of these three proteins in Gammarus pulex, during the embryonic development and the molt cycle of females. Results highlighted the presence of ecr and famet genes from the first stages of the embryogenesis, suggesting key roles in the embryo development. The mih gene was only measured from Stage 3 of embryogenesis, probably related to the gastrulation and the cephalothorax development. Regardless of the gene, a strong overexpression was also measured at the hatch time. Besides, differential expression levels of mih, ecr, and famet genes through the molt cycle were observed. The highest expressions of the three genes were measured at the premolt stage, confirming key roles of MIH and EcR in the ecdysteroid pathways, and also suggesting the involvement of the FAMeT enzyme during the ecdysis in G. pulex.